#3 Pressure Switch
WARNING: This page is about a different car, the 2009 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
Solenoid 2 signal fluid passes through the variable hi and 2-3-4 clutch regulator valve into the PS3 fluid passage. PS3 fluid opens the normally closed #3 pressure switch, signaling the TCM that the transmission is in Drive Range - Third Gear.